$\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}\left(\mathrm{s}\right)+2{\mathrm{S}}_2{\mathrm{O}}_3^{2-}\left(\mathrm{a}\mathrm{q}\right)\rightleftharpoons \mathrm{A}\mathrm{g}\left({\mathrm{S}}_2{\mathrm{O}}_3{)}_2^{3-}\right(\mathrm{a}\mathrm{q})+\mathrm{B}{\mathrm{r}}^{-}(\mathrm{a}\mathrm{q})$
Given ${\mathrm{K}}_{\mathrm{s}\mathrm{p}}\left(\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}\right)=5\times 10^{-13};{\mathrm{K}}_{\mathrm{f}}\mathrm{A}\mathrm{g}({\mathrm{S}}_2{\mathrm{O}}_3{)}_2^{3-}=5\times 10^{13}$
What is the molar solubility of AgBr in 0.1 M $\mathrm{N}{\mathrm{a}}_2{\mathrm{S}}_2{\mathrm{O}}_3$ ?

• A

  0.5 M
• B

  0.45 M
• Correct answer
  C

  0.045 M
• D

  None of these

Hence, the correct answer is option: 'C'.